Neuropeptide expression in rat paraventricular hypothalamic neurons that project to the spinal cord

The paraventricular hypothalamic nucleus (PVH) exerts many of its regulator y functions through projections to spinal cord neurons that control autonom ic and sensory functions. By using in situ hybridization histochemistry in combination with retrograde tract tracing, we analyzed the peptide expressi on among neurons in the rat PVH that send axons to the spinal cord. Project ion neurons were labeled by immunohistochemical detection of retrogradely t ransported cholera toxin subunit B, and radiolabeled long riboprobes were u sed to identify neurons containing dynorphin, enkephalin, or oxytocin mRNA. Of the spinally projecting neurons in the PVH, approximately 40% expressed dynorphin mRNA, 40% expressed oxytocin mRNA, and 20% expressed enkephalin mRNA. Taken together with our previous findings on the distribution of vaso pressin-expressing neurons in the PVH (Hallbeck and Blomqvist [1999] J. Com p. Neurol. 411:201-211), the results demonstrated that the different PVH su bdivisions display distinct peptide expression patterns among the spinal co rd-projecting neurons. Thus, the lateral parvocellular subdivision containe d large numbers of spinal cord-projecting neurons that express any of the f our investigated peptides, whereas the ventral part of the medial parvocell ular subdivision displayed a strong preponderance for dynorphin- and vasopr essin-expressing cells. The dorsal parvocellular subdivision almost exclusi vely contained dynorphin- and oxytocin-expressing spinal cord-projecting ne urons. This parcellation of the peptide-expressing neurons suggested a func tional diversity among the spinal cord-projecting subdivisions of the PVH t hat provide an anatomic basis for its various and distinct influences on au tonomic and sensory processing at the spinal level. J. Comp. Neurol. 433:22 2-238, 2001. (C) 2001 Wiley-Liss, Inc.